netdev - Re: [bpf PATCH 2/2] bpf, sockmap: fix incorrect fwd

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Date:   Thu, 25 Mar 2021 17:58:59 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        John Fastabend <john.fastabend@...il.com>
Cc:     Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...com>, bpf <bpf@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Lorenz Bauer <lmb@...udflare.com>
Subject: Re: [bpf PATCH 2/2] bpf, sockmap: fix incorrect fwd_alloc accounting

Cong Wang wrote:
> On Wed, Mar 24, 2021 at 7:46 PM John Fastabend <john.fastabend@...il.com> wrote:
> >
> > Cong Wang wrote:
> > > On Wed, Mar 24, 2021 at 2:00 PM John Fastabend <john.fastabend@...il.com> wrote:
> > > >
> > > > Incorrect accounting fwd_alloc can result in a warning when the socket
> > > > is torn down,
> > > >
> >
> > [...]
> >
> > > > To resolve lets only account for sockets on the ingress queue that are
> > > > still associated with the current socket. On the redirect case we will
> > > > check memory limits per 6fa9201a89898, but will omit fwd_alloc accounting
> > > > until skb is actually enqueued. When the skb is sent via skb_send_sock_locked
> > > > or received with sk_psock_skb_ingress memory will be claimed on psock_other.
> >                      ^^^^^^^^^^^^^^^^^^^^
> > >
> > > You mean sk_psock_skb_ingress(), right?
> >
> > Yes.
> 
> skb_send_sock_locked() actually allocates its own skb when sending, hence
> it uses a different skb for memory accounting.
> 
> >
> > [...]
> >
> > > > @@ -880,12 +876,13 @@ static void sk_psock_strp_read(struct strparser *strp, struct sk_buff *skb)
> > > >                 kfree_skb(skb);
> > > >                 goto out;
> > > >         }
> > > > -       skb_set_owner_r(skb, sk);
> > > >         prog = READ_ONCE(psock->progs.skb_verdict);
> > > >         if (likely(prog)) {
> > > > +               skb->sk = psock->sk;
> > >
> > > Why is skb_orphan() not needed here?
> >
> > These come from strparser which do not have skb->sk set.
> 
> Hmm, but sk_psock_verdict_recv() passes a clone too, like
> strparser, so either we need it for both, or not at all. Clones
> do not have skb->sk, so I think you can remove the one in
> sk_psock_verdict_recv() too.

Agree skb_orphan can just be removed, I was being overly
paranoid.

Thanks.